ARRANGEMENT OF BACTERIAL FLAGELLA

How Many Flagella Does a Bacterium Have?


How Are They Arranged?


There are basically four different types of flagellar arrangements:


1. A single flagellum can extend from one end of the cell - if so, the bacterium is said to be monotrichous.


2. A single flagellum (or multiple flagella; see below) can extend from both ends of the cell - amphitrichous.


3. Several flagella (tuft) can extend from one end or both ends of the cell - lophotrichous; or,


4. Multiple flagella may be randomly distributed over the entire bacterial cell - peritrichous.


Discrepancies in Definitions


amphi- a prefix meaning both or on both sides, as in amphimorphic.

Amphitrichous Microbiology, having a single flagellum at each end of the cell, as do certain bacteria. Also, amphitrichate. lopho- or loph- a combining form meaning a "ridge" or "tuft," as in lophodont, lophophore. lophotrichous Cell Biology, describing flagella that are arranged in a tuft at the pole of a cell.


amph(i)- [Gr. Amphi on both sides] a prefix meaning on both sides; around or about; double.
amphitrichous (am-fit¢ re-kus) [amphi- + Gr. thrix hair] having a single flagellum, or a single tuft of flagella, at each end; said of a bacterial cell. See flagellum.


loph(o)- [Gr. lophos ridge, tuft] a combining form denoting a relationship to a ridge or to a tuft.
lophotrichous (lo-fot¢ ri-kus) [lopho- + Gr. thrix hair] having two or more flagella at one or both ends; said of a bacterial cell. See flagellum.

KOCH'S POSTULATES

Four criteria that were established by Robert Koch to identify the causative agent of a particular disease, these include:


1.The microorganism or other pathogen must be present in all cases of the disease


2.The pathogen can be isolated from the diseased host and grown in pure culture


3.The pathogen from the pure culture must cause the disease when inoculated into a
healthy, susceptible laboratory animal


4.The pathogen must be re-isolated from the new host and shown to be the same as the
originally inoculated pathogen

THE MICROBIAL WORLD

The Nature of Host-Parasite Relationships between Bacteria and Animals

Interactions between Bacteria Humans

Bacteria are consistently associated with the body surfaces of animals. There are many more bacterial cells on the surface of a human (including the gastrointestinal tract) than there are human cells that make up the animal. The bacteria and other microbes that are consistently associated with an animal are called the normal flora, or more properly the "indigenous microbiota", of the animal. These bacteria have a full range of symbiotic interactions with their animal hosts.

In biology, symbiosis is defined as "life together", i.e., that two organisms live in an association with one another. Thus, there are at least three types of relationships based on the quality of the relationship for each member of the symbiotic association.

Types of Symbiotic Associations

1. Mutualism. Both members of the association benefit. For humans, one classic mutualistic association is that of the the lactic acid bacteria that live on the vaginal epithelium of a woman. The bacteria are provided habitat with a constant temperature and supply of nutrients (glycogen) in exchange for the production of lactic acid, which protects the vagina from colonization and disease caused by yeast and other potentially harmful microbes.

Lactobacilli in association with a vaginal epithelial cell (CDC).

2. Commensalism. There is no apparent benefit or harm to either member of the association. A problem with commensal relationships is that if you look at one long enough and hard enough, you often discover that at least one member is being helped or harmed during the association. Consider our relationship with Staphylococcus epidermidis, a consistent inhabitant of the skin of humans. Probably, the bacterium produces lactic acid that protects the skin from colonization by harmful microbes that are less acid tolerant. But it has been suggested that other metabolites that are produced by the bacteria are an important cause of body odors (good or bad, depending on your personal point of view) and possibly associated with certain skin cancers. "Commensalism" best works when the relationship between two organisms is unknown and not obvious.

Staphylococcus epidermidis (CDC).

3. Parasitism. In biology, the term parasite refers to an organism that grows, feeds and is sheltered on or in a different organism while contributing nothing to the survival of its host. In microbiology, the mode of existence of a parasite implies that the parasite is capable of causing damage to the host. This type of a symbiotic association draws our attention because a parasite may become pathogenic if the damage to the host results in disease. Some parasitic bacteria live as normal flora of humans while waiting for an opportunity to cause disease. Other nonindigenous parasites generally always cause disease if they associate with a nonimmune host.

Parasitology, actually a branch of microbiology, refers to the scientific study of parasitism but somehow it developed into a discipline that deals with eucaryotic parasites exclusively.

Bacterial Pathogenesis

A pathogen is a microorganism (or virus) that is able to produce disease. Pathogenicity is the ability of a microorganism to cause disease in another organism, namely the host for the pathogen. As implied above, pathogenicity may be a manifestation of a host-parasite interaction.

In humans, some of the normal bacterial flora (e.g. Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae) are potential pathogens that live in a commensal or parasitic relationship without producing disease. They do not cause disease in their host unless they have an opportunity brought on by some compromise or weakness in the host's anatomical barriers, tissue resistance or immunity. Furthermore, the bacteria are in a position to be transmitted from one host to another, giving them additional opportunities to colonize or infect.

There are some pathogens that do not associate with their host except in the case of disease. These bacteria may be thought of as obligate pathogens, even though some may rarely occur as normal flora, in asymptomatic or recovered carriers, or in some form where they cannot be eliminated by the host.

Opportunistic Pathogens

Bacteria which cause a disease in a compromised host which typically would not occur in a healthy (noncompromised) host are acting as opportunistic pathogens. A member of the normal flora can such as Staphylococcus aureus or E. coli can cause an opportunistic infection, but so can an environmental organism such as Pseudomonas aeruginosa. When a member of the normal flora causes an infectious disease, it sometimes referred to as an endogenous bacterial disease, referring to a disease brought on by bacteria 'from within'. Classic opportunistic infections in humans are dental caries and periodontal disease caused by normal flora of the oral cavity.

A photomicrograph of Pseudomonas aeruginosa, one of the most common opportunistic pathogens of humans. The bacterium causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia and a variety of systemic infections, particularly in cancer and AIDS patients who are immunosuppressed. CDC.

Infection

The normal flora, as well as any "contaminating" bacteria from the environment, are all found on the body surfaces of the animal; the blood and internal tissues are sterile. If a bacterium, whether or not a component of the normal flora, breaches one of these surfaces, an infection is said to have occurred. Infection does not necessarily lead to infectious disease. In fact, infection probably rarely leads to infectious disease. Some bacteria rarely cause disease if they do infect; some bacteria will usually cause disease if they infect. But other factors, such as the route of entry, the number of infectious bacteria, and (most importantly) the status of the host defenses, play a role in determining the outcome of infection.

Determinants of Virulence

Pathogenic bacteria are able to produce disease because they possess certain structural or biochemical or genetic traits that render them pathogenic or virulent. (The term virulence is best interpreted as referring to the degree of pathogenicity.) The sum of the characteristics that allow a given bacterium to produce disease are the pathogen's determinants of virulence.

Some pathogens may rely on a single determinant of virulence, such as toxin production, to cause damage to their host. Thus, bacteria such as Clostridium tetani and Corynebacterium diphtheriae, which have hardly any invasive characteristics, are able to produce disease, the symptoms of which depend on a single genetic trait in the bacteria: the ability to produce a toxin. Other pathogens, such as Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa, maintain a large repertoire of virulence determinants and consequently are able to produce a more complete range of diseases that affect different tissues in their host.

A photomicrograph of Corynebacterium diphtheriae bacteria using a Gram stain technique. Corynebacterium diphtheriae causes diphtheria that affects the upper respiratory tract, where an inflammatory exudate causes severe obstruction to the breathing airways, and sometimes suffocation. CDC.

Properties of the Host

The host in a host-parasite interaction is the animal that maintains the parasite. The host and parasite are in a dynamic interaction, the outcome of which depends upon the properties of the parasite and of the host. The bacterial parasite has its determinants of virulence that allow it to invade and damage the host and to resist the defenses of the host. The host has various degrees of resistance to the parasite in the form of the host defenses.

Host Defenses

A healthy animal can defend itself against pathogens at different stages in the infectious disease process. The host defenses may be of such a degree that infection can be prevented entirely. Or, if infection does occur, the defenses may stop the process before disease is apparent. At other times, the defenses that are necessary to defeat a pathogen may not be effective until infectious disease is well into progress.

Typically the host defense mechanisms are divided into two groups:

1. Constitutive Defenses. Defenses common to all healthy animals. These defenses provide general protection against invasion by normal flora, or colonization, infection, and infectious disease caused by pathogens. The constitutive defenses have also been referred to as "natural" or "innate" resistance, since they are inherent to the host.

2. Inducible Defenses. Defense mechanisms that must be induced or turned on by host exposure to a pathogen (as during an infection). Unlike the constitutive defenses, they are not immediately ready to come into play until after the host is appropriately exposed to the parasite. The inducible defenses involve the immunological responses to a pathogen causing an infection.

The inducible defenses are generally quite specifically directed against an invading pathogen. The constitutive defenses are not so specific, and are directed toward general strategic defense. The constitutive defenses, by themselves, may not be sufficient to protect the host against pathogens. Such pathogens that evade or overcome the relatively nonspecific constitutive defenses are usually susceptible to the more specific inducible defenses, once they have developed.

Special note. Most immunologists have subverted some of the "constitutive" defenses and moved them to the "inducible" category, although these defenses are not usually thought of as part of the immunological system. This refers to complement activation, the inflammatory response and the phagocytic response. Their reasoning is that these responses are, in fact, elicited or turned on by some chemical, physical or biological stimulation. However, the components or cells involved are constitutive components of the host. Nonetheless, these innate responses to pathogens may initiate, participate with, or otherwise affect an immunological response.

The Immune System

The inducible defenses are so-called because they are induced upon primary exposure to a pathogen or one of its products. The inducible defenses are a function of the immunological system and the immune responses. The constitutive defenses are innate and immediately available for host defense. The inducible defenses must be triggered in a host and initially take time to develop. The type of resistance thus developed in the host is called acquired immunity. The term immune usually means the ability to resist infectious disease. Immunity refers to the relative state of resistance of the host to a specific pathogen brought on by the activities of the immunological system.

Acquired immunity, itself, is sometimes divided into two types, based on how it is acquired by the host.

In active immunity, the host undergoes an immunological response and produces the cells and factors responsible for the immunity, i.e., the host produces its own antibodies and/or immuno-reactive lymphocytes. Active immunity can persist a long time in the host, up to many years in humans.

In passive immunity there is acquisition by a host of immune factors which were produced in another animal, i.e., the host receives antibodies and/or immuno-reactive lymphocytes originally produced in another animal. Passive immunity is typically short-lived and usually persists only a few weeks or months.

Antigens

Antigens are chemical substances of relatively high molecular weight, that stimulate the immune response in animals. Bacteria are composed of various macromolecular components that are antigens or " antigenic" in their host and bacterial antigens interact with the host immunological system in a variety of ways.

Natural Antibodies

Studies on germ-free animals have confirmed that a normal bacterial flora in the gastrointestinal tract are necessary for full development of immunological (lymphatic) tissues in the intestine. Furthermore, the interaction between these immune tissues and intestinal bacteria results in the production of serum and secretory antibodies that are directed against bacterial antigens. These antibodies probably help protect the host from invasion by its own normal flora, and they can cross react with antgenically-related pathogens. For example, antibodies against normal E. coli could react with closely-related pathogenic Shigella dysenteriae. These type of antibodies are sometimes called natural or cross-reactive antibodies.

Bacterial Antigens made into Vaccines

In another way, bacterial antigens that are the components or products of pathogens are the substances that induce the immune defenses of the host to defend against, and to eliminate, the pathogen or disease. In the laboratory, these bacterial antigens can be manipulated or changed so that they will stimulate the immune response in the absence of infection or pathology. These isolated or modified antigens are the basis for active immunization (vaccination) against bacterial disease. Thus, a modified form of the tetanus toxin (tetanus toxoid), which has lost its toxicity but retains its antigenicity, is used to immunize against tetanus. Or, antigenic parts of the whooping cough bacterium, Bordetella pertussis, can be used to induce active formation of antibodies that will react with the living organism and thereby prevent infection.

Antimicrobial Agents

One line of defense against bacterial infection is chemotherapy with antimicrobial agents such as antibiotics. The ecological relationships between animals and bacteria in the modern world are mediated by the omnipresence of antibiotics. Antibiotics are defined as substances produced by a microorganism that kill or inhibit other microorganisms. Originally, a group of soil bacteria, the Streptomyces, were the most innovative producers of antibiotics for clinical usage. They were the source of streptomycin, tetracycline, erythromycin and chloramphenicol, to name just a few antibiotics. Because bacteria evolve rapidly toward resistance, because bacteria can exchange genes for antibiotic resistance, and because we have overused and misused antibiotics, many pathogens are emerging as resistant to antibiotics. There have already been reported infections by Enterococcus, Staphylococcus aureus and Pseudomonas aeruginosa that are refractory to all known antibiotics. Bacterial resistance to antimicrobial agents has become part of a pathogen's determinants of virulence. These are examples of genetic means by which bacteria exert their virulence.

The usage of antibiotics to control the growth of parasites is an artificial way to intervene in the natural process of the host-parasite interaction. But, of course, it is done for the obvious purpose of curing the disease. The body heals itself: most antibiotics just stop bacterial growth, and the host must rely entirely on its native defenses to accomplish the neutralization of bacterial toxins or the elimination of bacterial cells. The judicious use of antibiotics in the past five decades has saved millions of lives from infections caused by bacteria.

BACTERIAL GROWTH

I. Nutritional (Chemical) Requirements


A. Energy source


1. sunlight:


2. oxidation:


B. Electron Transport


1. reduction of inorganic compounds:


2. reduction of organic compounds:

C. Carbon Source

1. carbon dioxide:

2. organic materials:



II. Physical (Environmental) Requirements


A. Oxygen:


1. aerobic:


2. microaerophilic:


3. aerotolerant:


4. facultatively anaerobic:


5. obligately anaerobic: Growth in Various O2 Concentrations

B. Temperature

1. Psychrophiles:

2. Psychrotrophs:

3. Mesophiles:

4. Thermophiles:

5. Hyperthermophiles:

C. pH

1. Acidophiles:

2. Neutrophiles:

3. Alkalophiles:

D. Pressure

1. Osmotic Pressure

a. facultative halophile:

b. extreme halophile:

2. Barametric Pressure

a. barotolerant:

b. barophile:

III. Natural vs. Laboratory Growth

IV. Processes and Measurement

A. Binary fission (log base 2)

N_(final) = N_(oiginal) x 2ⁿ

if n = # generations between original and final

then, log N_f = log N_o + n log 2,

B. Generation Time: g = t/n

where t = time between starting and final numbers.

Example

C. Measurement

1. dry weight:

2. direct count:

3. metabolic activity:

4. plate count:

5. turbidity:

Example

V. Eukaryotic Growth and Reproduction

A. Asexual-

B. Sexual-

VI. Viral Growth and Reproduction

A. Attachment:

B. Penetration:

C. Uncoating:

D. Biosynthesis:

E. Maturation:

STRUCTURE OF BACTERIA

Chemicals have properties. Biochemicals have both properties and ways of interacting with other chemicals eg. Fats vs. Carbohydrates. Fats form monolayers in water. Cell parts and Cells are the basic unit of life. They have attributes: Reproduction, metabolism, storage, transport, movement. We will look at a Prokaryotic cell from the outside in with an eye toward relating cell part properties to the biochemicals which compose them.

1. External Structures:

a. Glycocalyx or Capsule (computer slides)

1. Slime formation prevents dehydration.

2. allows for colony stability under adverse circumstances. Can be a big problem with biofilm development in catheters or industrial pipes. Dangerous source of infection in hospitals which is not readily removed by disinfection.

3. Non pathogenic organisms also have a capsule. Alcaligenes viscolactis is one of them.

4. Capsule can interfere with immune defenses of the host. It can interfere with phagocytosis. It swells during an infection, in many cases (Quellung reaction base of serological testing).

5. Streptococcus mutans sticks to teeth due to a capsule. Plaque becomes tartar if not removed.

6. Alcaligenes Viscolactis in milk.

b. Flagella--protein = flagellin. Anchored through the cell wall to a series of rings which rotate. Flagella is rigid and works more like an outboard motor than a whip. Must rotate thousands of times a minute in order to push cells with all that surface through water. 4mm to 6 mm per minute in E.coli. Flagella can rotate at 2500 rpm. All spirilla have flagella (axial filaments or endoflagella) about 1/2 of the bacilli and a few cocci.

DEFINITIONS:

4. Polar, lophotrichous, amphitrichous, peritrichous.

5. Runs and tumbles. Taxis, chemo, photo, thermo, magneto.

When a stimulus is present tumbles are inhibited and the flagella turns counterclockwise constantly toward the stimulus. This is positive taxis. When a substance initiates tumbles the cell's flagella go clockwise and the cell tumbles, resuming its run in another direction.

c. cell walls (exceptions--Mycobacterium, mycoplasma, archaebacteria, L-forms, spheroplasts, protoplasts.

1. Surrounding, encasing molecule is peptidoglycan. Visual.
NAM-NAG-NAM-NAG-NAM-NAG-NAM-NAG. This is the Glycan portion of peptidoglycan. Held together by beta linkages. Each Glycan strand held together by chain of amino acids to another strand. "Chain Link Fence" analogous.

2. Examine differences between Gram + and Gram - cell walls.

To the left is a gram stain of Staphylococcus epidermis done in our lab. The spherical cocci are tiny and are gram positive because they retain the primary stain crystal violet.

Below is a gram stain of a mixed culture of Micrococcus luteus (box like arrangements of cocci) with Escherishia coli. Micrococcus is gram positive while E.coli is gram negative. E. coli consists of very small delicate rods seen pink because they lose the primary stain as they are gram negative.

The gram negative cell wall of E. coli is much thinner than the wall of Micrococcus. Coli's cell wall also contains less peptidoglycan and more lipopolysaccharide.

3. Explain LPS and its role as an endotoxin and fever producer.

4. Also mention Spheroplasts and Protoplasts, L forms. Chlamydia and Rickettsia.

d. pili and fimbriae: Structures that allow sticking to surfaces---important in pathogenesis eg. UTI'"s, biofilms, teeth, glass, rocks (Pellicle formation in culture). Some Pili specialized. Sex pilus. 1946 experiment with minimal media showed genes transfered requiring contact. Define: auxotroph, prototroph, mutation rate. Minimal media (Glucose salts media). Mating types. F+ and F- (movie) e. other structures:


1. Chromatin Body--Long cirucular piece of DNA. Couple of thousand genes. It is haploid and relatively easy to manipulate eg...stick other genes into using bioengineering techniques.


2. Plasmids---small cirucular pieces of DNA (F factor is on a plasmid, Antibiotic resistance carried on plasmids). They are easily transferred from one cell to another. During sexual transfer recipient becomes F+.


3. Ribosomes---70s----50 + 30. Two parts. e. Mesosomes, endospores, fat globules, polyphosphate, Sulphur granules, magnetosomes, photosynthetic structures.


BIOCHEMICAL REACTIONS AND ENZYMES


I. Structure supports function. Function is physiology and metabolism. Metabolism is the sum of the biochemical reactions inside a cell. Lets take a closer look at how biochemical reactions or just ordinary chemical reactions occur.



A. Collision theory: This makes sense as an explanation of how two molecules may interact to form bonds. One bangs into another. If the collision is energetic enough--we see this as the reaction mixture being hot enough---or as Activation Energy---and if the vulnerable parts of the molecules are the ones that get hit, we get bonds breaking and new bonds forming.


H2O2 + I- ----> IO- + H2O IO-

+ H2O2 ----> O2 + H2O + I-


Two points should be made about the above reaction. It takes two steps to happen. I- is not used up in the reaction. The reaction occurs due to contact with I- where bonds are broken and new bonds formed. What bond is broken and what new bond forms? Also, I- is an inorganic small ion. Small inorganic species that speed reactions are called catalysts.



ENERGY DIAGRAM WITH AND WITHOUT A CATALYST


Define: Activiation Energy, catalyst (two examples), exergonic reaction, endergonic reaction. Show hydrogen peroxide and Iodide catalyst and catalase reaction. Explain how catalase identifies organisms Staph and Strep.

ENZYME ATTRIBUTES

1. Large protein molecules at approx 40,000 amu, Glucose substrate about 180 amu.

2. Denatured by heat--cooked potato vs. raw potato. Catalyst versus enzyme.

3. Lowers Activation energy by substrate binding at special place on the enzyme called the "Active Site"! There are other important sites on the enzyme but the active site is most important for catalysis.

4. Cofactors which bind and release from the Active site are often required (not always)...Vitamins and minerals act as cofactors. B vitamins often needed for energy reactions.

5 Efficient and able to process thousands of substrates per second. So only a small amount of enzyme needed to do reactions.

6. Can be interfered with. Example: Penicillin combines with an enzyme which is needed to put peptide cross links in cell wall material (Why is penicillin more active against gram positives?)

7. Delicate in that environmental conditions for use are narrow---pH, Temperature, Osmotic pressure, concentrations of substrates must be withing proper limits. Extremes can denature and kill cells.

FACTORS THE AFFECT THE ACTIVITY OF ENZYMES

1. TEMPERATURE

2. PH

3. CONCENTRATION OF SUBSTRATE

4. CONCENTRATION OF ENZYME

GRAPH THE AFOREMENTIONED VARIABLES AGAINST REACTION RATE..

ENZYME INHIBITION

1. Competitive Inhibition: Show succinic to fumaric acid and malonic acid inhibitor.

Succinic Acid Ž Fumaric Acid

Malonic Acid Inhibits the above reaction

2. Show structure of folic acid and PABA:

All inhibitors act at the active site. The inhibition is reversible by adding more substrate. New drugs are made which retain the properties of the inhibitor but which have new properties, like remaining in the urine longer etcetera.

When an inhibitor "looks like" the substrate of an enzyme it can inhibit it either reversibly or irreversibly. In irreversible inhibition the contact usually occurs in a place by covalent bonding and not just by stearic reactions.

Feedback Inhibition, Allosteric Inhibition, Endproduct Inhibition. Precursor Activation, Energy link control. Positive and Negative Feedback. All involve ligands and receptor.

INHIBITION AT THE LEVEL OF THE GENE.

FIRST DISCOVERED WAS THE LACTOSE ARRAY OF GENES THAT E.COLI HAS.

CALLED THE LAC OPERON--JACOB AND MONOD WORKED OUT THE MODEL: Wavy line made at R is repressor protein from R = repressor gene. I is the Incucer gene and a, b, c, and d are structural genes (make enzymes for lactose fermentation. Inducer can bind with repressor protein and "shut off".

I----a------------b--------------c--------------d-----------R------------> /\/\/\/\/\/\/\/

Structural genes for lactose

metabolism & repressor

(protein always on)(constitutive enzyme)

Another graphic with a promoter gene, which must be activated to turn system on:

LITHOTROPHS

PHOTOTROPHS

ORGANOTROPHS BREAK TO:

1. HETEROTROPHS (PARASITES, SAPROPHITES, Holotrophs)

2. Also Mutualistic bacteria and Commensals.

Metabolism is all reactions, break to:

A. Catabolic Reactions

B. Anabolic Reactions.

Example of catabolism is Glycolysis:

HISTORY OF MICROBIOLOGY

Best to think in terms of recurring themes:

1. Cause and cure of diseases

2. Nature of Putrefaction/Fermentation

3. Controversy over Spontaneous Generation.


Ancients felt the world filled with invisible spirits which would explain things we couldn't understand.


a. Death and Disease, Disability (there has to be a reason) WE STILL STRUGGLE WITH THESE THINGS IDEAS TODAY.


Greeks had anthropomorphic gods who interacted with them and could cause disease. Later Greeks lost faith in their gods and formulated other ideas. They were noted thinkers.


Example: Hippocrates--disease comes from an imbalance of intrinsic factors (nutrition) and extrinsic factors--air, exercise, etc.


Four elements of importance to balance: blood, phlegm, yellow bile, black bile. When these get out of balance problems occur. Bleeding to intervene. Today we infuse (add) blood with different ends in mind.


Hebrews and Egyptians believed in God and an afterlife. Some biblical accounts indicate that there was a vague notion of contagion developing --"Don't sleep in the House of a Leper". But also could get leprosy by angering the Lord. Angry Jewish God changed in Christianity. Jewish God brought plagues famines and disease to Egyptians, for example.



Aristotle and others believed in abiogenesis. Life came from inanimate material. Myths among many ancient people talk of the origin of man, even, from decaying corn. Shakespeare wrote about crockadiles coming from the mud of the Nile.



Van Helmont wrote recipe for mice---dirty underwear, corn, in a vessel---mice come out fully formed. Solves another inexplicable problem: The origin of life.
Until this is properly understood we could never understand contagion. 1546



Fracastorius of Verona wrote of contagium vivum--immersed in a syphilis epidemic at the time. Other terms "Seminaria morbi". Described transmission through inanimate objects--fomites--Through air--"ad distans" and through direct contact. Work is ignored, no evidence for any of this. It just made sense to him.


1609 Janssen and Galileo grind lenses to produce low resolution microscopes---microorganisms below the resolution achieved. But improvements were to come.


Hooke--Discovers cells with an improved microscope.



Schleiden and Schwann discover all plants and animals are composed of cells.
1650's Leewenhoek--Delft Holland in the textile industry and part time lens grinder. Got good resolution to allow about 3 or 4 hundred X useful magnification. He put hay and pepper into water and then looked at it through his microscope. He saw microbes in an infusion as seen below.



Leewenhoek saw bacteria, protozoa, yeasts and described all the microbial forms we now know, except for viruses. Although he is not mentioned in the science literature as observing his animalcules divide, nevertheless he believed spontaneous generation was untrue and in his original papers called the idea a "bad joke" as related by Dr. Moll at the University of Amsterdam.

Left Image depicts a hay infusion. Hay is placed in pure water for a few days and protozoa, bacteria, fungi, and algae develop. The larger cells on the left are ciliate protozoa. The small rod shaped organisms in single and pairs are bacteria. The image was made black and white at Northwestern to save space. This is likely very close to what Leewenhoek saw in the 17th Centrury.



Francesco Redi, in the 1700's did a simple experiment to show flies needed parents. Used cheesecloth screening and meat.

Spallanzani, a monk, in the first part of the 18^th Century boiled and sealed broths. When he was careful no microbes developed. His work was criticized by Needham, a Welchman of the Royal Society in that other factors, excluded by Spallanzani, were needed for Sp. Gen. Notably air. Needham performed similar experiments, sloppily executed, in which microbes grew from contamination.

Spallanzani died before he could clearly disprove Needham.

Louis Pasteur, a noted chemist, took up the challance and utilized broths allowing air but disallowing microbes. Grew broths at different altitudes and in a dusty cellar. Used broths with cotton to show the germs accumulated on cotton. Did the Swan neck tube experiment.

Ignaz Semmelweis, an eastern european physician working in a Vienna Hospital, noticed the wards where delivery occurred by midwives had 10X less Puerperal Fever and deaths than those tended to by doctors. He showed he could dramatically decrease "Childbed Fever" by having doctors wash hands in chlorine water after dissection of cadavers and between patients. Was fired for blaming deaths on doctors who didn't wash hands.

Oliver Wendel Holmes wrote on the Contagiousness of Puerperal Fever". Author, Physician, and Anatomy Professor. Late 19^th Century.

Lister used antiseptics on wounds and during surgery. He showed they healed much faster with the antiseptic treatment. Was also the first to isolate a pure culture by serial dilution: Bacterium lactis.

Pasteur wanted to isolate a bacterium in pure culture that caused disease. Began working with Anthrax.

Robert Koch in Germany did too. He worked with various preparations to provide solid culture media. A woman working in his lab tried agar, recommended by a cook who used it to solidify puddings because it stayed solid at warm temps. Koch was using sterile potato slices for media.

Koch isolated anthrax and formulated his Postulates.

Pasteur went to work on chicken cholera and discovered one could attenuate cultures and produce artifical vaccines.

Pasteur solved the riddle of rancid wines in France's vinyards. Recommended sterile technique and Pasteurization (applied to milk and became a central method for controling TB, Diptheria, and other diseases).

Weinogradski and others showed soil bacteria recycle nutrients.

Chamberland developed a bacterial filter. Resulted in:

a. discovery of viruses

b. discovery of toxins

Pasteur produced attenuated rabies virus and rabies vaccination procedure. Tried it on Joseph Meister. It worked.

During the 20^th Century we have:

1. Development of viral culture techniques and attenuation

2. Development of the electron microscope.

3. Discovery of antibiotics (Fleming and Dubos)

4. Discovery of Prions (Pruissner)

5. Bioengineering--removal and replication of genes--incorporating them into microbes and switching them on.

6. DNA vaccines

7. Antiviral Compounds--ribivirin, protease inhibitors.

8. Translation of the entire genome of some microorganisms e.g. yeast.

All not rosy---reemergence of infectious diseases a constant problem. St Louis Encephalitis, West Nile Virus, Lyme disease, AIDS, Hanta virus Sin Nombre,Ebola outbreaks, E. coli, Antibiotic resistant bacterial strains and so on.